1877.] 



System of the Brain. 



333 



the ordinary preparation by chrome hardening, and the subsequent 

 staining with logwood, carmine, and other dyes (adopting Lockhart 

 Clarke's method for clearing and mounting), I have struck out inde- 

 pendently a series of investigations devoted to the preparation of the 

 brain in the fresh state, feeling convinced that the disuse of hardening 

 agents would eliminate many sources of fallacy. A method was adopted 

 by me and described at length in the ' Monthly Microscopical Journal ' 

 (Sept. 1876), whereby the cells and cortical structure generally could be 

 well displayed. The great fault attached to this process is that relation- 

 ships were wholly sacrificed for clearer definition of structure and differ- 

 entiation of elements. Having endeavoured, without success, to obtain 

 satisfactory results by the ordinary freezing methods with ice and salt, 

 I eventually devised an instrument whereby freezing with ether spray 

 was introduced, and all the conditions requisite for cutting the finest 

 sections of fresh brain were obtained. This instrument was made for me 

 by Mr. Baker of High Holborn, and is described by me in the ' Journal 

 of Anatomy and Physiology ' for April 1877, and proves to be of the 

 greatest value in the investigation of nervous structures. 



When perfectly fresh sections of healthy brain are thus obtained, and 

 the slightest possible staining of the nerve-cells produced by a drop of 

 carmine, or a *25 per cent, solution of aniline black, just sufficing, in fact, 

 to give us the outline of the cells, nuclei, nucleoli, and their environment, 

 we are able to detect, in most cases, indications of spaces surrounding 

 the cell ; and especially is this the case in conditions which induce a shrink- 

 ing of the cell-protoplasm, or, on the other hand, of the surrounding 

 neuroglia. 



The examination of these films of fresh cortex by chemical reagents, 

 their examination after staining by aniline and mounting in balsam, the 

 process of teasing above alluded to, as well as chrome hardening for sec- 

 tions, have been the methods employed in this investigation. 



EXPLANATION OF THE PLATES. 

 Plate 1. 



Fig. 1. Section obtained from the ascending frontal gyrus of a healthy young cat. 



Illustrative of the relationships of the pericellular lymph-sacs to the blood- 

 vessel and its lymphatic sheath (the brain in this case was hardened and 

 stained simultaneously). X 180 diameters. 



Fig. 2. Section from the frontal lobe of a kitten at birth. Exhibits the young nerve- 

 cells of the cortex within their lymphatic sacs arranged along the perivas- 

 cular channels. The neuroglia is finely granular, the perivascular sheaths 

 are distended, and the nerve-cells fail to exhibit clear indications of a 

 nucleus. X 210 diameters. 



Fig. 3. Similar appearances shown in a section obtained from the same convolution in 

 a dog at birth. The nerve-cells are becoming elongated, pyriform, and in 

 some cases exhibit a nucleus. X 210 diameters. 



